The manipulation of fluids to form fluid streams of desired configuration, discontinuous fluid streams, particles, dispersions, etc., for purposes of fluid delivery, product manufacture, analysis, and the like, is a relatively well-studied art. For example, highly monodisperse gas bubbles, less than 100 microns in diameter, have been produced using a technique referred to as capillary flow focusing. In this technique, gas is forced out of a capillary tube into a bath of liquid, the tube is positioned above a small orifice, and the contraction flow of the external liquid through this orifice focuses the gas into a thin jet which subsequently breaks into equal-sized bubbles via a capillary instability. In a related technique, a similar arrangement was used to produce liquid droplets in air.
Microfluidics is an area of technology involving the control of fluid flow at a very small scale. Microfluidic devices typically include very small channels, within which fluid flows, which can be branched or otherwise arranged to allow fluids to be combined with each other, to divert fluids to different locations, to cause laminar flow between fluids, to dilute fluids, and the like. Significant effort has been directed toward “lab-on-a-chip” microfluidic technology, in which researchers seek to carry out known chemical or biological reactions on a very small scale on a “chip,” or microfluidic device. Additionally, new techniques, not necessarily known on the macro scale, are being developed using microfluidics. Examples of techniques being investigated or developed at the microfluidic scale include high-throughput screening, drug delivery, chemical kinetics measurements, combinatorial chemistry (where rapid testing of chemical reactions, chemical affinity, and micro structure formation are desired), as well as the study of fundamental questions in the fields of physics, chemistry, and engineering.
The field of dispersions is well-studied. A dispersion (or emulsion) is a mixture of two materials, typically fluids, defined by a mixture of at least two incompatible (immiscible) materials, one dispersed within the other. That is, one material is broken up into small, isolated regions, or droplets, surrounded by another phase (dispersant, or constant phase), within which the first phase is carried. Examples of dispersions can be found in many industries including the food and cosmetic industry. For example, lotions tend to be oils dispersed within a water-based dispersant. In dispersions, control of the size of droplets of dispersed phase can effect overall product properties, for example, the “feel” of a lotion.
Formation of dispersions typically is carried out in equipment including moving parts (e.g., a blender or device similarly designed to break up material), which can be prone to failure and, in many cases, is not suitable for control of very small dispersed phase droplets. Specifically, traditional industrial processes typically involve manufacturing equipment built to operate on size scales generally unsuitable for precise, small dispersion control. Membrane emulsification is one small scale technique using micron-sized pores to form emulsions. However, polydispersity of the dispersed phase can in some cases be limited by the pore sizes of the membrane.
Batch production of discontinuous fluids are prone to difficulties in product uniformity. These problems can be compounded for complex structures such as double emulsions (drops-in-drops) or triple emulsions (drops-in-drops-in-drops). A further difficulty for double or triple emulsions is poor encapsulation efficiency, where substantial amounts of the innermost phase leak out into the outermost phases, which can limit the usefulness of such emulsions as carriers for valuable or volatile compounds such as drugs, flavors, or fragrances. Microfluidic devices, by contrast, can produce multiple emulsions with extremely high uniformity and encapsulation efficiency, essentially by regulating emulsion formation on the individual-droplet level. Such control comes at the cost of forming emulsion droplets essentially one at a time, each microfluidic device producing only small amounts of product on the order of fractions of a milliliter per hour. The present invention in part involves appreciation of the need for scale-up of the products of microfluidic devices.
While many techniques involving control of multi-phase systems exists, there is a need for improvement in control of size of dispersed phase, size range (polydispersity), and other factors.